Some basic supplies you'll need are the terrarium, of course, a set of artificial lights, and a fan to circulate air inside the terrarium. One thing that can be useful is mylar or another reflective material to line at least 3 out of the 4 sides of the container. This will help increase the amount of light your plant gets from the artificial lights. Raisers to keep your plants out of the water that will collect at the bottom of the terrarium will also be helpful. What types of plants do you plan on putting inside?
I am planning to relocate my entire collection of carnivorous plants into a (TBA) gallon tank which are Nepenthes Ventricosa, Nepenthes Sanguinea, Drosera Aliciae, Drosera Capensis, Ultricularia Sandersonii and two Pinguicula Moranensis (one appears to look really weird but healthy).
Honestly I wouldn't bother with putting any of those into a terrarium. None of those species require particularly high humidity and the nepenthes will get too large to be housed inside the terrarium within a year or two. If you're moving your plants off the windowsill I'd recommend setting up a rack with lights to hold your plants. A lot simpler, and simplicity is always good when possible.